Referring to FIG. 8, a prior art zipper is illustrated. In this prior art, the lower stop has a block 81 and a pin 82. Moreover, in FIG. 9, another prior art zipper is illustrated. The lower stop of the zipper has a block 91 and a pin 92. For the prior art shown in FIG. 9, the block 91 has a channel 911 for fixing a lower portion 926 of a pin 92. An upper end of the block 91 has a buckle 912 which can be buckled into the high portion 927 of the pin 92. The feature of the prior art is that an inner lateral wall of the high portion is installed with a longitudinal rib 925. A buckling groove 914 formed by two tenons 913 at an inner surface of the buckling portion 912 so as to achieve the function of retaining and releasing-proof.
Referring to FIG. 10, it is illustrated the defect of the prior art. In the prior art zipper, the lower stop 9 can be used to Nylon zipper or plastic steel zipper, wherein the block 91 and the pin 92 are installed at a lower end of the chain tooth 93 and are fixed to the inner lateral sides of the left and tight teeth strips 94. A lower end of the pin 92 has inclined edges 921 and 922 at two sides thereof. Thereby, the lower end can be inserted into the channel 911. However only the tapered edge 923 at the upper end of the inclined surface 922 is in contact with the inner wall of the channel 911. Further, the buckling portion 912 of the block 91 has two tenons 913 at inner wall of the upper end thereof. The two tenons 913 can engage the longitudinal rib 925 at the inner wall of the pin 92. Besides, a top of the pin 92 has a recess 924 for guiding the tooth head 931 of the chain tooth 93.
With reference to FIG. 11, a schematic view showing the lower stop of the prior art zipper suffers from a force. In general, the lower stop must suffer from a pull force of 9 kg/cm2 (which is art international standard). The pull force can be divided into a vertical pull force, an upper pull force, a lower pull force and a lateral pull force. In general, the lower stop can match the standard. However because some nations adapts a high standard (15 kg/cm2), the lower stop can not match this standard. Especially, the lateral pull force can not match this standard. This is because when the strips 94 are pulled by lateral forces (as indicated by arrows), in the pin 92 of the lower stop, only the projection 923 and the recess 924 suffer from pull forces. Although the recess 924 is stopped by the tooth head 931 of the chain tooth, the chain tooth 93 will extend due to the action of the chain strips 94 so as to move abnormally. When the applied force is larger, the tooth head 931 will separate from the recess 924 so that the pin 91 releases. When the applied force is larger, the tooth head 931 will release from the recess 924. As a result, the upper end of the pin 91 is released to move outwards. Next, the projection 923 at the lower end displaces inwards after it displaces outwards at an upper end of the pin 91 so that the projection 923 releases from an upper end of the channel 911. Thereby, the pin 91 releases, rotates and looses.
With reference to FIG. 12, an inner side of the channel 911 of the block 91 is installed with a sliding groove 915, the sliding groove 915 will cause the inner side of the block 91 can not suffer from a vertical clamping force (as shown by the arrow). Therefore the inner side of the block 91 breaks from the portion between the middle line 916 (indicated by the dashed line) and the channel so that the lower stop can not be used.